Sully (left) and Mike don’t live up to the expectations set in “Monsters Inc.” Photo: Everett Collection

“My job isn’t to make mediocre students slightly less mediocre students,’’ says the dean in “Monsters University,’’ the third under-achieving animated feature in a row from the once-great Pixar Animation Studios.

My job, as I see it, isn’t to overpraise mediocre animated features like this one, a needless and largely charmless prequel to the 2001 hit “Monsters Inc.,’’ which directly preceded Pixar’s remarkable run of Oscar-winning animated classics — “Finding Nemo,’’ “The Incredibles,’’ “Ratatouille’’ “Wall-E’’ and “Up.’’

The mildly amusing “MU’’ — which has Mike (basically a giant green eyeball voiced by Billy Crystal) and the hulking gorillabear Sully (John Goodman, also returning) meeting at the titular institution — is less an awful movie than a totally uninspired one. The under-5 set may find it funny, though I suspect their parents will be checking their watches a lot, as I did.

In “Monsters University,” a younger Mike (left) faces a confrontation with the dean, voiced by Helen Mirren. (Everett Collection)

Family entertainments often get graded on a curve by lazy and condescending movie critics. But not always. My colleague Kyle Smith lambasted Pixar’s abysmal “Cars 2’’ with 1 ¹/₂ stars and Sara Stewart gave the trite and timid “Brave’’ 2 stars.

“MU’’ is yet another play-it-safe cash grab that doesn’t aspire to come within light years of even the second tier of Pixar titles — including the three “Toy Story’’ films and the original “Cars’’ — all of which had genuine multigenerational appeal, if not quite the level of sophistication of the studio’s classics.

I’d apply that label as well to “Monsters Inc.,’’ which I gave 3 ¹/₂ stars 12 years back. It had a winning premise — a world of monsters that lie just beyond the closet doors of kids everywhere waiting to scare them — and reams of clever dialogue.

“MU’’ largely discards that clever setup — human kids are barely seen till the end — in favor of a generic “Revenge of the Nerds’’ knockoff, and tosses out the original supporting cast except for Steve Buscemi’s chameleon, who has what amounts to a glorified cameo.

The cowardly and not-at-all frightening Mike and the not-too-bright Sully, scion of a family of famous scarers, start off bickering endlessly at first. But eventually they lead a team of misfits in the Scare Games — which they need to win to stay in the School of Scaring.

The sad sacks in the Oozma Kappa Fraternity — including a fat, balding, middle-aged ex-salesman and a literal blob whose mom owns the frat house — seem designed, like the movie, more to sell toys than to create engaging characters.

Helen Mirren voices the dean — an imposing centipede-like creature with wings — but mostly director Dan Scanlon and his team wastes her vocal talents on dull expository dialogue instead of quips that might entertain adults.

It’s the sort of toon where you’re always 20 minutes ahead of the story, which is often repetitious and badly in need of editing.

Things pick up a toward the end, when the movie suddenly turns into a fairly clever horror-movie parody with some human characters. This sequence is so utterly different in tone from the rest of “MU’’ that it feels like something Pixar added at the last minute to keep audiences from nodding off.

There was a time not so long ago when Pixar’s annual feature was an eagerly anticipated event. And you’d never, ever mistake them for the more formulaic product mass-produced by their rivals at Walt Disney Feature Animation or DreamWorks Animation.

It’s hard not to blame the precipitous decline in Pixar’s quality and ambition on its 2006 acquisition by bottom-line obsessed Disney, which formerly had served strictly as Pixar’s distributor.

Pixar features put into production after that, like “Monsters University,’’ seem primarily aimed at making tons of money — not that anything’s wrong with that. But it’s something that was never true in those glorious days when Pixar was reinventing feature animation.